The most distant thing most people can see without a telescope is the Andromeda Galaxy, 2.537 million light years away. When you look at Andromeda, the photons making up the light you're seeing left that galaxy before humans had even evolved on planet Earth.
But things travelling at the speed of light don't experience time. From the perspective of those photons, they left Andromeda and arrived in your eye in the exact same moment.
Another of the most distant things you can see with your own eyes is the Triangulum Galaxy. At 2.73 million light years away, it's a bit more distant than Andromeda, but much harder to see without good eyesight and very dark skies
Triangulum much fainter than Andromeda, because it's less massive, contains fewer stars, and doesn't have the same bright core that Andromeda has. It also contains no central supermassive black hole – and no one knows why. It's kinda weird.
The most distant things human eyes can see are these four galaxies.
Messier 81, 8.5 million light years away. Sculptor, 11.4 million light years away. Centaurus A, 12.4 million light years away. And Messier 83, 14.7 million light years away.
Though you'd need sharp eyes to see these yourself, and skies which are both exceptionally dark and clear.
When light was leaving Messier 83, actual mastodons were still alive on Earth, the Sahara wasn't a desert, and cats didn't exist yet.
